Tubular waveguide used as an amplifier



TUBULAR WAVEGUIDE USED-AS AN AMPLIFIER Filed May 16, 1962 2 Sheets-Sheetl United States Patent 3,332,030 TUBULAR WAVEGUIDE USED AS AN AMPLIFIERJack Fajans, Douglaston, N.Y., assignor to Electrokinetics gorporation,Florham Park, N .J a corporation of New ork Filed May 16, 1962, Ser. No.195,209 9 Claims. (Cl. 330-62) This invention relates to tubularwaveguides for highfrequency electromagnetic oscillations, and moreparticularly to waveguide for transmitting, generating, and amplifyingoscillations of extremely short wavelengths, including wavelengths ofthe order of millimeters.

In my copending application Ser. No. 162,457, filed on Dec. 27, 1961,now abandoned, I have disclosed negative resistance devices based on theuse of magneto-resistive materials, the term being applied to conductivematerials which respond to an applied magnetic field with an increase intheir electrical resistance, and to a decrease in the intensity of theapplied magnetic field with an increase in electrical conductivity. Ihave now found that the negative resistance devices of my earlierinvention impart highly desirable characteristics to waveguides in whichthey are employed as structural elements.

Propagation of an electromagnetic wave along a conventional waveguide isordinarily accompanied by attenuation of the wave in the longitudinalguide direction Z. The electric field components may be represented byan equation of the following known type.

wherein a is the attenuation factor;

to is the angular frequency of the wave;

is 211- times the reciprocal of the guide wavelength; and jis the squareroot of minus one.

Normally, the attenuation factor at has a positive value because oflosses at the Walls of the guide, in the guide dielectric, at joints,etc. I have found that these losses can be balanced by making at least aportion of the waveguide of a material having a negative resistance.When a major portion of the waveguide walls is made of negativeresistance material the Waveguide acts as an amplifier, and may beoperated as a generator of electromagnetic waves.

The attenuation factor a for a coaxial line is expressed by thefollowing equation (from Ramo and Whinnery, Fields and Waves in Radio,2nd edition, Wiley, 1953, page 39):

wherein R, L, and C respectively are the resistance, inductance, andcapacitance of the line per meter of length, and G is the conductanceper meter due to leakage current.

For the purpose of this discussion, G may be assumed to be negligible.Equation 2 then assumes the form It is evident that a is negative when Ris negative.

The general object of this invention is a waveguide having a negativeattenuation factor.

The exact nature of this invention as Well as other objects andadvantages thereof will be readily apparent from consideration of thefollowing specification relating to the annexed drawing in which:

FIG. 1 shows a first embodiment of the waveguide of the invention in anaxially sectional fragmentary view;

FIG. 2 is a perspective fragmentary view of an element of the waveguideof FIG. 1 on an enlarged scale;

FIG. 3 shows another embodiment of the waveguide of the invention incross section transversely of its axis; and

FIG. 4 shows a modification of the embodiment illustrated in FIG. 1 in acorresponding view.

Referring now to the drawing in detail, and initially to FIG. 1, thereis shown a coaxial line having a straight main portion 1 consisting of acylindrical tubular outer conductor 2 of tin-plated copper and an innerconductor 3. Plugs 4 and 5 of conducting material are axially slidablein the elongated space or cavity Within the outer conductor and havecentral apertures in which the inner conductor 3 is supported on annularinsulators 41, 51 respectively. The impedance of the waveguideillustrated may be matched in a conventional manner by axial movement ofthe plugs 4, 5.

The structure of the inner conductor 3 is better seen from FIG. 2. Theconductor 3 consists of three coaxial layers which are partly brokenaway in order better to reveal the manner in which they aresuperimposed. The innermost layer or core 31 is a lead wire of 10microns diameter. The wire is covered by a layer 32 of silicon monoxide,approximately one micron thick which acts as an insulator separating thecore 31 from an outer tubular conductor 33 having an approximatethickness of one micron, and consisting of tin. The exposed face of theouter conductor is parallel to the direction of elongation of thecavity.

Leads 34, 35 are conventionally represented, and are conductivelyattached to axial end portions of the core 31. They are connected to asource of electric current in such a manner that current flows throughthe leads 34, 35 and the core 31 in the direction of the arrows 36. Avariable resistor 30 in the lead 34 permits the current to becontrolled. Leads 37, 38 attached to terminal portions of the outertubular conductor 33 are connected to a second source of current so thatcurrent flows in the leads 37, 38 and the tubular conductor 33 in thedirection of the arrows 39. In the binary coaxial conductor constitutedby the insulated conductive core 31 and the outer conductor 33, the twocurrents flow in opposite directions.

The portions of the conductor 3 to which the leads 34, 35, 37, 38 areattached are not seen in FIG. 1 which only illustrates an intermediateportion of the waveguide and adjacent parts of the longitudinallyterminal portions thereof. Coaxial lines or waveguides 6, 7 areconnected respectively to these terminal portions for coupling the mainportion 1 of the coaxial line to a source of electromagneticoscillations and to a load. An electromagnetic field may thus begenerated in one of the terminal portions of the waveguide cavity, andan electromagnetic signal may be transmitted to the load from the otherterminal portion. The outer conductors 62, 72 of the lines 6, 7 areconnected to the outer tubular conductor 2, and the corresponding innerconductors 63, 73 are conductively joined to the inner conductor 3, andmore specifically, to the outer tubular tin layer 33.

The entire apparatus seen in FIG. 1 is held in a cryostat at atemperature of 2.0 K., that is, lower than the transition temperaturesof lead and tin which are respectively 7.22 K. and 3.73 K. In theabsence of magnetic fields, both the core 31 and the outer conductor 33of the inner conductor 3 are superconductors since they are held at atemperature lower than their transition temperature.

A current of 0.8 ampere is caused to flow through the lead core 31 inthe direction of the arrows 36. The magnetic field generated by thecurrent flow is sufficient to destroy the superconductivity of the outertin conductor 33, but does not affect the superconductive state of thelead core 31. A small potential applied by means of the leads 37, 38causes a current of 0.25 ampere to flow through the outer tin conductor33. The resulting magnetic field reduces the primary magnetic fieldgenerated by the current in the lead core 31 sufiiciently to restore thesuperconductivity of the tin layer 33. The voltage applied to the tinlayer may then be reduced to Zero without changing the conductive stateof the apparatus.

A signal of a frequency for which the waveguides have been matched bymeans of the plugs 4 and 5 is now admitted through line 6 from anantenna of a conventional type, not further illustrated. The mainportion 1 of the waveguide has a length of approximately 20 centimeters.

The signal is emitted through the coaxial line 7 at an increasedamplitude, and may be fed to a transmitting antenna.

The apparatus shown in FIG. 1 thus constitutes an amplifier in whichnegative resistance is induced in the outer tin layer 33 by the currentsflowing therein and in the core 31. The apparatus may be connected to asource of electromagnetic waves other than the afore-mentioned receivingantenna, and drive a load other than a transmitting antenna. Theamplifier is capable of operating at very short wavelengths which arelimited only by the performance of the materials of constructionemployed. When tin is used as the outer lay-er of the inner conductor,the amplification factor of the device begins to decrease atapproximately 10 cycles per second, but other magnetoresistive materialsmay be substituted for tin, and the apparatus may thereby be adapted tooperation as an amplifier for waves having a length of a fewmillimeters. Lead as a core material may be replaced by a superconductorwhich is not affected by even strong magnetic fields, such as niobium,and other variations and modifications of the apparatus illustrated willfollow from the considerations set forth in more detail in my citedcopending application.

FIG. 3 illustrates a rectangular waveguide of conventional outerappearance, the waveguide being shown in section at right angles to itslongitudinal axis. The four flat longitudinal walls of the waveguideeach consist of three layers, and corresponding layers of the walls areintegrally joined to each other.

The innermost layer 11 consists of tin, the outer layer 12 is vanadium,and the interposed layer 13 insulates the layers 11, 12 from each otherand consists of silicon monoxide. Conductors and current sourcesproviding currents flowing in opposite longitudinal directions throughthe two conductive layers of the waveguide walls have not beenillustrated since they do not differ materially from those shown in FIG.2. It will also be understood that the waveguide shown in FIG. 3 isequipped with means for coupling the same to a source of electromagneticoscillations and to a load. The operation of the apparatus illustratedin FIG. 3 is the same as described above with reference to FIGS. 1 and2.

The embodiment of the invention shown in FIG. 4 is similar to thatillustrated in FIG. 1. It differs from the latter by an interruption inthe main portion of the tubular outer conductor 2 of the waveguide. Thegap between the two axially separated sections 2, 2 of the outer tubularmember is bridged by impedance matching horns 2a, 2b of substantiallyconical shape respectively coaxially secured to the tubular sections 2',2" and flaring toward each other in a well known manner.

Oscillations are transmitted by a conventional waveguide of the typeshown in FIG. 4 when the gap measures a few feet or even one hundredfeet. I have found that the permissible length of the gap may beincreased substantially under otherwise comparable conditions when theaxial conductor of the conventional arrangement is replaced by aconductor 3 which has a negative resistance. This conductor may beidentical with the conductor 3 shown in FIG. 1 and in more detail inFIG. 2.

When the gap between the sections 2', 2 is of the order of a few feet, asignal received by the waveguide arrangement of FIG. 4 over the coaxialline 6 is emitted through the coaxial line 7 with increased amplitude.As this art progresses, the amplification factor of the arrangement andthe permissible length of the gap between the tubular sections 2', 2"may be expected to be increased.

When the conductor 63 is removed from the cylindrical waveguides shownin FIGS. 1 and 4, and the plug 4 is advanced into the main portion ofthe waveguide, the same capable of operating as a generator oroscillator producing a high-frequency signal emitted over the coaxialcable 7.

It should be understood of course that the foregoing disclosure relatesto only a preferred embodiment of the invention, and that it is intendedto cover all changes and modifications of the example of the inventionherein chosen for the purpose of the disclosure which do not constitutedepartures from the spirit and scope of the invention set forth in theappended claims.

What I claim is:

1. A waveguide arrangement comprising, in combination:

(a) electrically conductive wall means defining an elongated space,

(1) a face portion of said wall means contiguously adjacent said spacebeing parallel to the direction of elongation of said space;

(b) means for generating an electromagnetic field in a longitudinallyterminal portion of said space;

(0) means outside said space for inducing negative resistance to saidfield in said face portion; and

(d) means for withdrawing an electromagnetic signal from the otherlongitudinally terminal portion of said space,

(1) said face portion being at least partly interposed between saidterminal portions and being elongated in said direction,

(2) said means for inducing negative resistance. including a source of afirst magnetic field, a source of an electric current, said face portionconsisting essentially of electrically conductive magneto-resistivematerial arranged in said magnetic field and responsive to a decrease inthe intensity of said magneticfield to reduce the electrical resistivityof said material, and means for connecting said source of electriccurrent to said face portion for passage of said current throughsaidportion in a direction to generate a second magnetic field opposed tosaid first magnetic field.

2. An arrangement as set forth in claim 1, wherein said face portion isof superconductor material, said arrangement' further comprising meansfor keeping saidv face portion at a predetermined temperature lower thanthe transition temperature thereof, and said first magnetic field beingof an intensity sufiicient to destroy the superconductivity of saidsecond conductor. at said predetermined temperature.

3. An arrangement as set forth in claim 1, wherein saidspace is ofannular cross section and said face portion is convex to define theinner dimension of said space transverse of the direction of elongationthereof.

4. An arrangement as set forth in claim 1, wherein said space is ofpolygonal cross section, and said face portion defines at least one sideof said cross section.

5. An arrangement as set forth inclaim 1, wherein said space is ofrectangular cross section, the four sides of said cross section beingdefined by said face portion.

6. A waveguide arrangement comprising, in combination, a first tubularconductive member and a second tubular conductive member, said membershaving a common axis and being axially spaced from each other, each ofsaid members defining an axial cavity therein; impedance matching hornmeans axially extending from each of said members in a direction towardthe horn means on the other member; and an elongated conduct-orcoaxially arranged in said axial cavities, and longitudinally extendingbetween said cavities, at least a portion of said elongated conductorhaving negative resistance.

7. A Waveguide arrangement as set forth in claim 6, wherein said portionof said elongated conductor is outside said axial cavities.

8. A waveguide arrangement as set forth in claim 6, further comprising asource of a first magnetic field; a source of an electric current, saidconductor portion consisting essentially of electrically conductivemagneto-resistive material arranged in said field and responsive to adecrease in the intensity of said field to reduce the electricalresistivity of said material; and means for connecting said source tosaid conductor for passage of said current through said portion thereofin a direction to generate a second magnetic field opposed to said firstmagnetic field.

9. A Waveguide arrangement comprising, in combination:

(a) electrically conductive Wall means defining an elongated space (1) aface portion of said wall mens contiguously adjacent said space beingparallel to the direction of elongation of said space;

(b) means for generating an electromagnetic field in a longitudinallyterminal portion of said space;

(c) means outside said space for inducing negative re sistance to saidfield in said face portion; and

(d) means for withdrawing an electromagnetic signal from the otherlongitudinally terminal portion of said space.

(1) said face portion being elongated in said direction and extendingfrom one of said terminal portions to the other terminal portion.

References (Iiteil UNITED STATES PATENTS OTHER REFERENCES TheNegative-Conductance Slot Amplifier, by Pedinofi" IRE Transactions onMicrowave Theory and Techniques, pp. 557-566, November 1961.

ROY LAKE, Primary Examiner.

NATHAN KAUFMAN, Examiner.

1. A WAVEGUIDE ARRANGEMENT COMPRISING, IN COMBINATION: (A) ELECTRICALLYCONDUCTIVE WALL MEANS DEFINING AN ELONGATED SPACE, (1) A FACE PORTION OFSAID WALL MEANS CONTIGUOUSLY ADJACENT SAID SPACE BEING PARALLEL TO THEDIRECTION OF ELONGATION OF SAID SPACE; (B) MEANS FOR GENERATING ANELECTROMAGNETIC FIELD IN A LONGITUDINALLY TERMINAL PORTION OF SAIDSPACE; (C) MEANS OUTSIDE SAID SPACE FOR INDUCING NEGATIVE RESISTANCE TOSAID FIELD IN SAID FACE PORTION; AND (D) MEANS FOR WITHDRAWING ANELECTROMAGNETIC SIGNAL FROM THE OTHER LONGITUDINALLY TERMINAL PORTION OFSAID SPACE, (1) SAID FACE PORTION BEING AT LEAST PARTLY INTERPOSEDBETWEEN SAID TERMINAL PORTIONS AND BEING ELONGATED IN SAID DIRECTION,(2) SAID MEANS FOR INCLUDING NEGATIVE RESISTANCE INCLUDING A SOURCE OF AFIRST MAGNETIC FIELD, A SOURCE OF AN ELECTRIC CURRENT, SAID FACE PORTIONCONSISTING ESSENTIALLY OF ELECTRICALLY CONDUCTIVE MAGNETO-RESISTIVEMATERIAL ARRANGED IN SAID MAGNETIC FIELD AND RESPONSIVE TO A DECREASE INTHE INTENSITY OF SAID MAGNETIC FIELD TO REDUCE THE ELECTRICALRESISTIVITY OF SAID MATERIAL, AND MEANS FOR CONNECTING SAID SOURCE OFELECTRIC CURRENT TO SAID FACE PORTION FOR PASSAGE OF SAID CURRENTTHROUGH SAID PORTION IN A DIRECTION TO GENERATE A SECOND MAGNETIC FIELDOPPOSED TO SAID FIRST MAGNETIC FIELD.